Hey - recently acquired a Siglent SDS1202X-E oscilloscope for some geek-ed out stuff I’ve been working on not related anything plasma cutting. Not an expert on it yet by any means, but a light bulb went off today thinking about some of the issues I’ve had in the past with THC lifting up.
I’ve been wishing there was a feature to measure/log voltage over time in the Firecontrol app - but it occurred to me…duh…that’s what oscilloscopes do - measure signals/voltage over time…I’ve not hooked up mine YET, but before I do, wondering if anyone has played around with this? I’m thinking about tapping into the 50:1 signal and logging data onto a usb stick. Anyone done this already?
The 50:1 signal is probably ok to use. I wouldn’t use raw voltage as the return is probably not Grounded (most likely connected to the Work lead) and I’d be concerned about damaging your scope.
Good info - thanks. Yeah - I’m still getting my head fully around some of the grounding stuff - I got a cheap differential probe that will isolate the probes/ground and should work ok…but I’ve not done anything at these voltages yet, so I’m sure I’ll let some magic smoke out somewhere along the way…hopefully not…should be some fun learning if I don’t make stuff go boom…
I’m not sure what Differential ‘probe’ is, but, yes, if you measure differentially then it would be the difference between the Work Clamp voltage and the raw Arc voltage and that would be safe. Good on you!
You’ll probably not see more than a very noisy, DC, varying level. For the THC, I believe they filter it with chokes and capacitance up front and then apply a noise cancelling algorithm (DSP) before employing it as a feedback signal.
I’ve had a scope on my list for a long time - I a hobbyist/ham/advanced amateur - so justification has been a little rough, but it went on sale during Amazon Prime day - $315 - figured I’d not see that price again for a while…
mostly want to play around with the CAN bus on my vehicles and some arduino/iot stuff…
Assuming you have not already hooked up your scope, I would suggest you not do so until you measure the potential between the 50:1 divider outputs and ground with a voltmeter. Even if you use a differential probe, it will likely have a maximum “common mode” voltage wrt ground that shouldn’t be exceeded. If you don’t use a differential probe, you need to make sure what ever you hook the reference lead to is at ground potential. I have both a Miller and a Hypertherm cutter and the manual for neither one gives any indication of how far offset the divider outputs are from ground. Looking at the circuit diagrams for both, which do not include complete detail, I’d say there is a good chance the work clamp, and hence one side of the divider, is at whatever potential the work is at, not at the potential of the electrical supply ground.
Classic Tek 465 you’ve got there, I used to work with & on them in Beaverton. I’m only slightly more modern with a 2225. There’s something about an old analog scope, I miss my old bench 7904 with 7A26/7B53.
As for measuring the torch voltage, definitely go with the 50::1 and DC coupling. With your scope’s sample rate and memory you should be able to sweep fairly slowly and zoom in after the fact, just hit the stop trigger when you see a problem.
Thanks - yeah that’s exactly what I’ve been trying to make sure before I link it all up…I think I’ve got my head around the grounding now…also was considering getting a cheap battery operated scope I saw on Amazon for around $60 that would make it a bit safer, but I think the diff probes will provide the isolation I need.
Showoff! This was my baby back before your 545. I had it filled with a quad channel plugin in both bays. A VERY early predecessor to an 8 channel logic analyzer (with the advantage of being analog). I was the only one on the engineering team who could run it
I used it to synchronize events coming from a Gamma camera where the input came in at random times, but had to be pulled out of a FIFO to be stored synchronously in memory. Good fun, that one!
Now That is a classic! I worked on a couple of that vintage way back when.
As for the cheap scope, how about a data logger? Amazon has some that will let you go USB to a PC, then you won’t have to try to get the trigger just right, $60 for 40k samples/second one channel.
- so justification has been a little rough, but it went on sale during Amazon Prime day - $315 - figured I’d not see that price again for a while…
